In 1962, he began starring in the television series Combat! as Platoon Leader 2nd Lt. Gil Hanley, probably his most memorable role. The show memorably also starred Vic Morrow as Sgt. Chip Saunders and Conlan Carter as Doc. Combat! was a hit and lasted for five seasons and 152 episodes.

After retiring from screen appearances, Jason kept busy by doing voice-overs for commercials and wrote his autobiography, Scrapbooks of My Mind. In 2000, he attended a Combat! reunion in Las Vegas with fellow cast members.[2]